The present invention relates to a lumbar support device mounted in a seat back of a vehicle seat.
A lumbar support device in a vehicle seat back is used for adjusting the firmness of the seat back in order to reduce the fatigue of an occupant or seated person who sits on the seat of a vehicle for a long time. To this end, the lumbar support device is usually provided with a support or lumbar plate which can be moved in a horizontal direction and a vertical direction by operating a lever connected thereto to align it with the lumbar region of the occupant of the seat.
The lumbar support device of this kind is known in a prior art, as disclosed in the Examined Japanese Utility Model Publication No. 1-30121(1989). This lumbar support device includes a crank rod turnably supported on a seat back frame and a support member slidably supported on the crank rod.
In this device of the prior art, the support member is moved forward and backward of the seat back to adjust a degree of pressure or hardness for supporting the lumbar region of a seated person, by activating the crank rod by a first drive mechanism, which is supported on the seat back frame, that is, by turning the crank rod with respect to the seat back frame. The support member is moved upward and downward of the seat back to adjust the position for supporting the lumbar region of the seated person, by activating a second drive mechanism, which is also supported on the seat back frame, that is, by sliding the support member with respect to the crank rod.
In the aforementioned device of the prior art, however, the first drive mechanism and the second drive mechanism for moving the support member longitudinally and vertically of the seat back are supported by the seat back frame. In order that the turns of the crank rod may not be obstructed by the second drive mechanism, therefore, there has to be set a play mechanism between the second drive mechanism and the seat back frame. This play mechanism may increase the number of parts to complicate the structure and to increase the chattering of the support member.